Solvent effect on H-bond cooperativity factors in ternary complexes of methanol, octan-1-ol, 2,2,2-trifluoroethanol with some bases

Abstract

Cooperative hydrogen bonds in ternary complexes (ROH)2⋯B (ROH-alcohols; B-bases) formed in pure bases (B) and solutions in n-hexane, carbon tetrachloride, benzene and 1,2-dichloroethane were studied by FTIR spectroscopy. Based on the observations, the authors were able to propose an original method of evaluating solvent effects on cooperativity factors in the complexes. Frequencies of cooperative hydrogen bonds OH⋯B (νb) were determined for ternary complexes of pyridine with aliphatic alcohols (methanol, octan-1-ol) and for 2,2,2-trifluoroethanol with three different bases (acetonitrile, diethyl ether, tetrahydrofuran). The solvent shifts of νb were found to correlate with an empirical thermochemical parameter of the solvent, SVW. The cooperativity factors were determined for the complexes (ROH)2⋯B in all studied media. It has been found that the cooperativity factors are almost independent of the solvent. In addition, a method was proposed of estimating the frequencies and cooperativity factors for ternary complexes (ROH)2⋯B in the gas phase. It has been found that in gas phase the cooperativity factors are practically the same as in condensed media. © 2007 Elsevier B.V. All rights reserved.